Process of coloring wood veneers and the like



Patented June 2, 1936 UNITED STATES PATENT OFFICE PROCESS OF COLORINGWOOD VENEERS AND THE LIKE No Drawing. Application May 31, 1934, SerialNo.

728,381. In Canada June 24, 1933 1 Claim.

This invention relates to improvements in the process of coloring, byimpregnation, wood veneers and similar thin pieces of wood throughoutthe thicknesses of the veneers, and has for its ob-' 5 ject to produce auniformity of coloring of the veneers under low cost conditions not onlyavoiding deleterious eiiects upon the veneers but also obviating anynecessity of drying the colored veneers.

Prior attempts have been made to satisfactorily color veneers throughoutthe thickness thereof, by boiling the veneers in alkaline solutions, orby steaming, necessitating subsequent drying of the impregnated veneersand rendering them subject to checking or cracking. It has also, beenfound, in the prior employment of the boiling or steaming processes,that the veneers treated in the usual bundles are not uniformly coloredthroughout the width thereof, showing light centers and imperfectionsalong the grain margins. In other prior attempts to color wood byimpregnation, the woodhas been fumed by ammonia gas under temperatureand pressure conditions resulting in an undesirable refrigerating 2action during the introduction of the ammonia gas into the woodcontainer, and in deleterious effects upon the wood.

According to the present improved procedure,

the wood veneers are first dried and preferably to an extent beyond thefiber-saturation point" of approximately 20% moisture content, i. e.,the

veneers are preferably dried to have approximately only 4% moisturecontent. The dried veneers are piled upon a truck or other supportproviding for convenient introduction of the veneers into a cylinder orreceptacle having a door or doors which may then be closed, thereceptacle.

being vented to the outside atmosphere. When piling the veneers upontheir support, superposed 40 sheets of the veneers built up to athickness of approximately one inch or slightly less are separated fromthe next overlying veneers by suitable spacing strips. By means ofsuitable steam pipes or coils within the closed receptacle into whichthe veneers are placed, the temperature within the receptacle is raisedby heat radiation and convection at atmospheric pressure to a degreeinsuring a rapid evaporation of the veneer moisture, a preferredtemperature attained being approximately 250 F. It will be understood,of'course, that by raising the temperature in the receptacle asmentioned, the veneers will be correspondingly heated throughout theirthickness to a corresponding degree. While somewhat lower or highertemperthe gas in the receptacle atures than the specified temperaturemay be employed with corresponding variations in the subsequentimpregnation time, it has been determined that a temperature of 250 F.is highly efllcient for the coloring operation, and is not harm- 5 fulto the veneers under the improved coloring conditions.

When the receptacle temperature has been raised to the degree mentioned,superheated ammonia gas is introduced into the receptacle, said 10 gaswhen so introduced having approximately the same temperature as orslightly higher than that within the receptacle, and the quantity of gasintroduced being approximately 25 lbs. per 1000 board feet of veneers.By heating the'ammonia l5 gas before introduction into the receptacle toapproximately thereceptacle temperature, the reirigerationtendency dueto the expansion of is minimized. While other means may be employed forproviding the 0 heated ammonia gas, it is preferred to generate the gasfrom aqua ammonia in an evaporator disposed externally adjacent to thereceptacle, the heating of the aqua ammonia to approximately 255F.developing a generated gas pressure in 25 the evaporator sufiicient tocause a natural flow of the heated gas into the preheated receptacle andwithout materially raising the pressure in said receptacle aboveatmospheric pressure. The pressure developed in the receptacle by thegas 30 introduction is preferably controlled by a suitable pop valve toconfine it to the nominal amount of 1 to 2 lbs. gauge, and preferablydoes not exv ceed 5 lbs. gauge as a maximum, it being sufiicient todevelop a slight indicated gauge pressure 5 merely to insure that thereceptacle is filled with ammonia gas. Because of the pressure developedin the evaporator by the generated ammonia gas only a negligiblequantity of water vapor is carried into the receptacle with the ammoniagas, the 40 superheated condition of any water vapor carried into thereceptacle maintaining the dry condition within the receptacle.

. While it is preferred to employ the above described preheated ammoniagas supplying means, a substitute therefor comprises injecting, forinstance aqua ammonia, into an evaporating pan within the receptacle togenerate the ammonia gas directly within the receptacle heated byinternal radiation and convection. It is to be un- 0 derstood, however,that the temperature of 250 F. initially attained within the cylindershould preferably be maintained substantially constant during theintroduction of, the ammonia gas into the cylinder, and that thereceptacle pressure 55 medium providing for ready absorption 01' theammonia gas by the veneers, the ammonia gas reacting with the wood acidsto color the veneers uniformly throughout-their thickness, and the heatconditions above described favoring the chemical reaction resulting inthe coloring of the veneers.

After the ammonia gas has been introduced into the receptacle asdescribed, the previously attained temperature of 250 F. and the nominalpressure before mentioned are maintained substantially constant forapproximately 12 hours,

- after which the veneers are removed. Any pressure drop due to gasabsorption by the veneers may be compensated for by introduction intothe receptacle of slightly more ammonia gas. The specified time of 12hours may be somewhat varied by a corresponding change in the receptacletemperature, as has been previously noted.

It will be apparent that the described veneercoloringprocess isperformed under dry conditions such that the moisture content of thepreviously dried veneers is not increased, whereby the colored veneersare ready for use without any further drying operations. The dryconditions mentioned also materially lessen deterioration oi thereceptacle, heretofore incident to the relatively wet methods employedfor coloring veneers. The veneers are not only uniformly colored, but notrimming of the veneer edges is requiredv to cut away any softened ordiscolored margins present in prior practised methods of coloringveneers. A particular advantage residing in the practising of thedescribed coloring process, is

that uniformity of coloring is attained in successive runs of the.veneers, and accordingly the coloring may be practised on a commercialbasis. Furthermore, the short time required to eflect the coloringoperation is still another factor in the low cost of production.

Having thus set forth the nature of the invention, what I claim hereinis:-

The process of coloring wood veneers, consist-p ing in loading into areceptacle veneers having a moisture content below the fiber-saturationpoint, raising the temperature within the receptacle by dry heat'and atsubstantially atmospheric pressure to approximately 250 F. to completelyvaporize the moisture content of the veneers, introducing into theheated receptacle approximately 25 lbs. of preheated ammonia gas per1000 board feetof veneers, said ammonia gas having been preheated toapproximately the temperature within the receptacle, and maintaining theattained temperature oi substantially 250 F. and the substantiallyatmospheric pressure constant within 'the receptacle for a definitecoloring period.

- FRANK G. BRIGHT.

